Project Summary In this application, we describe a population of adipose cells that appear to be ILC as they lack expression of CD3, MHCII, and NK1.1. Interestingly, these ILC-like cells co-express high levels of the transcription factors PLZF and ROR?t. The study of these newly identified adipose PLZF, ROR?t cells is the focus of this R21 application. Our colleague at Rutgers found that the FDA approved metabolic uncoupling anthelmintic treatment, niclosamide ethanolamine (NEN), shows promise for the treatment of Type 2 Diabetes. NEN proved to be highly effective in treating symptoms arising from two different mouse models of diabetes. This included preventing weight gain, increased fasting blood glucose and basal plasma insulin. NEN also improved insulin sensitivity in these models. We carried out exploratory experiments to determine if NEN treatment altered the frequencies or phenotype of adipose resident lymphocytes after mice were fed high fat diet. The results of these analyses led to the identification of the adipose PLZF,ROR?t ILC. Of particular interest was that the adipose PLZF,ROR?t ILC from mice fed high fat diet expressed CD44, suggesting activation in response to conditions associated with the onset of obesity and metabolic syndrome. Remarkably, when treated with NEN, CD44 upregulation was prevented, suggesting that part of the mechanism by which NEN prevents Type 2 Diabetes is immune system mediated. There is a growing understanding that lymphocytes contribute to maintenance of an anti-inflammatory environment and thermogenic programs in adipose tissues. The continued effort to define the function of all lymphocyte subtypes in the fat will clearly be essential for understanding these processes. If successful, this grant will identify a new lymphocyte population that, based upon preliminary data, might control adipose tissue immune homeostasis and thermogenesis. Such cells types continue to open new possibilities for the treatment of a major health problem. In this R21 application we propose to study a novel population of innate-like cells that simultaneously express high levels of PLZF and ROR?T. The characterization of this population of cells expressing two transcription factors that display such specific and function-oriented expression in the immune system will greatly enhance our understanding of the cellular subsets that regulate the adipose microenvironment. Of particular note here is that this population expresses an activation-associated phenotype (increase in CD44 expression) in response to high fat diet that is abrogated in response to treatment shown to diminish diet-induce metabolic dysregulation. This drug (NEN) is already approved for use in humans for the treatment of helminth infection. Therefore, successful completion of the experiments described in this proposal has the potential for rapid translation to immunotherapy to combat obesity and metabolic diseases.